Ferroelectric phase shifters are used to control the phase of an electromagnetic wave such as a microwave or a millimeter wave signal. This changing of the phase or phase shifting makes possible the steering of an electromagnetic beam without physically moving an antenna. Phase shifters are extensively used in electronic scanning radar. An array of phase shifters are used to steer the electromagnetic wave front without any mechanical movement.
It is desirable to electronically control the phase shift that a given device can produce. One such device that provides a controlled variable phase shift is disclosed in U.S. Pat. No. 5,032,805 entitled "RF Phase Shifter" and issuing to Elmer et al on Jul. 16, 1991, which is herein incorporated by reference. Therein disclosed is a phase shifter made from a ceramic material, the permitivity of which may be varied by varying the strength of an electric field to which it is subjected or immersed. The phase shift is continuously varied by varying the applied voltage from a single source. This phase shifter, while providing variable phase shifts, requires a relatively complex voltage source with associated control circuits. Another phase shifter that reduces the control circuits previously required is disclosed in U.S. Pat. No. 5,307,033 entitled "Planar Digital Ferroelectric Phase Shifter" issuing to Koscica et al, the same inventors as the present invention, on Apr. 26, 1994, which is herein incorporated by reference. Therein disclosed is a planar stripline type ferroelectric phase shifter that has a plurality of series coupled independent ferroelectric phase shifting elements. Each element has a different length and is coupled to a separate voltage source for separately controlling each separate ferroelectric element. This results in a discrete phase shift for providing a desired cumulative phase shift. This digital ferroelectric phase shifter has the advantage of requiring less complex control or drive circuits. However, the physically separated lengths of ferroelectric material result in a relatively complex structure that is difficult and costly to fabricate.
While the above ferroelectric phase shifters have advanced the art, they are not appropriate in many applications. Therefore, there is a need for ferroelectric phase shifters that are simpler, and easier and less costly to fabricate and manufacture. Reducing the fabrication cost of each ferroelectric phase shifter is particularly important in view of the large numbers of ferroelectric phase shifters required in a typical array as used in an electronically scanning radar device.